1. Field of the Invention
The present invention relates generally to optical elements. More particularly, the present invention is related to optical devices used to transform a small or point light source into an area light emitter.
2. Description of Related Art
A generic problem in optical design is how to transform small or point sources of light into area light patterns such as linear or cylindrical. With the development of small, high brightness light sources such as inorganic and organic Light Emitting Diodes (LEDs), the problem of developing such optical systems has become particularly relevant. LEDs are typically very smallxe2x80x94on the order of 0.25 mm to 0.50 mm on a sidexe2x80x94and are very efficient and reliable. Furthermore, LEDs have been produced with luminous efficiencies of over 100 lumens/watt, and it is likely that LEDs will continue to improve as light sources. In order to take advantage of small high brightness light sources such as LEDs, research has now embarked on ways to utilize these light sources in applications that require linear and area light outputs.
Optical transformer devices are described herein that are useful for providing a variety of area output patterns from a small light source. Such devices can be made efficient, which advantageously provide low energy consumption and long battery life. Furthermore such devices can be reliable and manufactured at low cost. The optical transformers have a wide variety of possible uses such as room and task illumination, theatrical lighting, optical communications emitters, automotive lamps, biomedical light injectors, backlights and frontlights for LCD displays, and any application in which unusual and nonconventionally shaped light sources would be useful.
A light ejector for transversely ejecting substantially collimated light injected by a light source, comprises a plurality of partially reflective interfaces arranged along a central axis, the partially reflective interfaces also arranged symmetrically at a nonzero angle with respect to the central axis, so that substantially collimated light injected by the light source in a direction approximately longitudinally along the central axis travels through each of the partially reflective interfaces, providing an area light output that comprises light reflected from each of the partially reflective interfaces. The partially reflective interfaces may be arranged for providing Fresnel reflectance or may comprise metallic or dielectric coatings that provide partial reflectance.
A variety of embodiments are described. In one embodiment the length between adjacent interfaces is at least long enough that light reflected from any of the interfaces does not interact with any adjacent interface. Embodiments are described in which the light ejector comprises a cylindrical configuration, a rectangular block configuration, or an N-sided polygonal configuration.
The light ejector may be formed of a plurality of stacked cones, each cone comprising a male end and a female end, the plurality of cones stacked so that the junction between a male end of one cone and a female end of an adjacent cone defines the partially reflective interface.
In one embodiment the interfaces comprises a zigzag configuration, each interface comprising an inner interface proximate to the central axis and an outer interface distal from the central axis, the inner interfaces angled to eject light traveling in a first longitudinal direction, and the outer interfaces angled oppositely to eject light traveling in a second, opposite longitudinal direction. In one such embodiment the light ejector comprises a cylindrical configuration, and the light source provides an annular beam that is injected into the outer interfaces along the second direction, and further comprises a turning reflector formed on the ejector on the side opposite the light source, the turning reflector having a configuration to reverse direction of the injected beam along the first direction and redirect it into the inner interfaces.
In some embodiments, on the side opposite the light source, a turning reflector is provided arranged to reverse the direction of light incident thereon. In addition, some such embodiments also comprise a polarization retarder situated to rotate polarization of longitudinally traveling light. The polarization retarder may comprise an optically active material, or a Kerr device, a Pockels device, or a Faraday effect device. An embodiment is described in which the turning reflector and polarization retarder comprise a grooved reflector. The grooved reflector may comprise a spiral configuration or a plurality of parallel grooves.
An embodiment is described in which the ejector comprises a stripe ejector in which the partially reflective interfaces are parallel and angled to provide an output configuration in the shape of approximately a stripe. The stripe ejector can be used with a holographic optical component arranged to receive the stripe output and direct it to an LCD display, thereby front lighting the LCD display.
Still other embodiments are described in which the interfaces are formed in a sawtooth configuration, the ejector including an upper plate that has a plurality of rows of teeth, and a lower plate has a plurality of rows of teeth that engage with the teeth in the upper plate.
The ejector can be used by itself or with other optical components. In one embodiment, an annular reflector is arranged around the ejector to receive light output from the ejector and redirect it to provide an emitter.
The ejector described herein can be adapted for a wide variety of uses. For example the ejector can be designed to transform randomly polarized light sources into complex of linearly polarized sources. The ejector can be designed to create a wide range of geometric-shaped beam patterns such as triangle, rectangle, and N-sided polygons from collimated light sources. The ejector can be employed in high speed optical communication emitters that are inherently susceptible to noise from phantom radiation sources.